FIG. 13 is a view showing the structure of a conventional polarizing beam splitter.
When light having a P-polarization and an S-polarization in a mixed state is incident upon a polarizing beam splitter (PBS) 1, the P-polarization is transmitted through the polarizing beam splitter 1 and the S-polarization is reflected by the polarizing beam splitter 1.
The reflected S-polarization and the transmitted P-polarization are directed in the same direction by diamond-shaped prisms 2 and 3.
For example, the P-polarization is transmitted through the prisms and is then changed into an S-polarization by a half wave plate (retarder) 4.
As a result, the light having the P-polarization and the S-polarization in the mixed state is changed into the same polarization, e.g. the S-polarization, by the polarizing beam splitter. That is, the light having the P-polarization and the S-polarization in the mixed state has the same direction.
The operation principle of a stereoscopic image device using the conventional polarizing beam splitter is as follows. U.S. Pat. No. 7,857,455 is referred to.
As shown in FIG. 14, light emitted from an imaging surface 5 for generating an image in a projector passes through a projection lens 6 and is then split into two beams by a polarizing beam splitter 7.
That is, light having an S-polarization component and a P-polarization component is reflected by the polarizing beam splitter 7, or is transmitted through the polarizing beam splitter 7.
The transmitted P-polarization component is changed into S-polarization while passing through a half wave retarder 8. The S-polarization is concentrated on a projection screen via reflective members 9 and 10, a polarizer 11, and a modulator 12.
The modulator 12 may change a polarization direction depending on, for example, an electric signal.
On the other hand, the S-polarization reflected by the polarizing beam splitter 7 reaches the projection screen via a reflective member 13 in a state in which the S-polarization is maintained in the same direction.
Consequently, the light, having mixed polarization directions, emitted from the imaging surface 5 is changed into a single S-polarization.
However, the stereoscopic image device using the conventional polarizing beam splitter has the following problems.
A left-eye image and a right-eye image are alternately emitted from the imaging surface 5. The images are displayed on the screen via the above-described elements. In a case in which a single projector is used to provide a stereoscopic image, parallax occurs when the left-eye image and the right-eye image are provided.
In addition, light projected by a single projector is split depending upon a polarization state of the light, and optical energy is consumed when the light is incident upon the screen. As a result, the luminance of the light is low.